The invention relates to circuitry for digitally monitoring analog parameters, such as temperature, pressure or the like, of industrial installations such as turbines and boilers.
Monitoring circuits commonly used in such applications are arranged to produce a plurality of constant-amplitude pulses which are proportional in some way to the instantaneous analog value of the installation quantity to be monitored. Typically, such pulse sequence may be processed in a central computer, which provides control signals to maintain the value of the monitored analog parameter within a required range.
The most common of such monitoring circuits involve the use of relay-type facilities, which in practice have tended to wear quickly and to malfunction under severe ambient conditions of temperature, humidity, vibration and dust. Moreover, such relay-type arrangements are relatively bulky and complex, and consume an inordinate amount of power.
Another common embodiment of such circuit has involved the use of photoelectric techniques. Such facilities have the disadvantage of being relatively inaccurate; moreover, the required lamp sources have been found to have a relatively short life, so that frequent maintenance is necessary.